Outpatient treatment of cocaine dependence is associated with a high drop- out rate and frequent relapse to cocaine use. Relapse to cocaine abuse is often triggered by alcohol use. Naltrexone has shown promise in treatment of alcoholism and may have efficacy in the treatment of cocaine dependence by reducing alcohol-triggered relapse. This application proposes a 16- week, placebo-controlled, double-blind, randomized clinical trial to test the efficacy of naltrexone in reducing relapse to cocaine abuse in cocaine abusers who drink alcohol. One hundred subjects with DSM-III-R diagnoses of cocaine dependence and alcohol dependence or abuse will be randomly assigned to receive either 50 mg of naltrexone or placebo daily. Subjects will receive medication for four months; follow-up evaluations will be conducted at months 5 and 6. Study medication will be added to comprehensive, recovery-oriented, outpatient chemical dependency treatment. This study will be conducted at the drug treatment program of Summit Medical Center, a not-for-profit private hospital in Oakland, CA. Following completion of baseline measures, subjects will be assessed weekly to determine their compliance with study medications, to ascertain their use of alcohol, cocaine or other drugs, to complete rating scales, have a breathalyzer test, give an observed urine specimen, and receive their next week's supply of study medication. Data collection instruments will include the Addiction Severity Index, the Profile of Mood States, the Symptom Checklist-90, and the Treatment Services Review. Primary efficacy measures are: days of cocaine use, treatment retention, cocaine craving, and alcohol use. Pre-planned analyses will use survival analysis and analysis of variance to compare naltrexone and placebo and gender by study drug interaction.